BAI Ruxia,LIU Hai,WANG Yushu,HUANG Jianguo.Heavy Metal Contents in Eupatorium Adenophorum in Liangshan of Sichuan, and Safeness of Using the Plant as Organic Manure[J].Acta Pedologica Sinica,2018,55(2):432-442

Heavy Metal Contents in Eupatorium Adenophorum in Liangshan of Sichuan, and Safeness of Using the Plant as Organic Manure

BAI Ruxia, LIU Hai, WANG Yushu, HUANG Jianguo

College of Resources and Environment, Southwest University

Abstract:

【Objective】Eupatorium adenophorum, an alien perennial plant of Compositae, native of Central America invaded China extensively via Myanmar in the 1940s. The invasive plant is now widespread in farmlands, forests, and pastures in tropical and subtropical areas of Southwest China, such as Yunnan, Guizhou, Guangxi, Sichuan and Tibet, covering as high as about 20% of the total land in certain regions and causing enormous economic loss and serious ecological calamities, because of its strong ability to adapt various environments. Therefore, E. adenophorum is considered to be the most harmful invasive plant in this country. To control overspreading of the invasive plant, prevention in combination with utilization could be one of the most economical and effective ways. It is necessary to point out that E. adenophorum is no good to be used as pulp, building materials, fuel, and animal food because this plant is short of fiber, weak in rupture strength, and low in combustion value, and contains chemicals noxious to animals. However, this harmful plant is rich in organic matter and mineral nutrient, such as nitrogen, phosphorus, potassium, and microelements. Bio-composting of the plant through inoculation of certain specific microbes can kill the reproductive organs of the plant and decompose the chemicals contained in E. adenophorum noxious to animals, microbes, and other plants. Its content of heavy metals is the critical issue for the plant to be used as source of organic manure. 【Method】Samples of E. adenophorum plants, soils, neighboring plants and in-situ bio-composted E. adenophorum plants were collected from 42 E. adenophorum colonies in lands of mining, agriculture, forestry and transportation typical of Liangshan, Sichuan for analysis of contents of Pb, Cd and Cr using an atomic absorption spectrophotometer, and contents of Hg and As using an atomic fluorescence spectrophotometer in order to evaluate safeness of utilizing E. adenophorum as source of organic manure. 【Result】Results show that heavy metals in the plants varied sharply, exhibiting a sequence of Cr (x ̅=14.17 mg kg-1) > Pb (x ̅=4.55 mg kg-1) > Cd ( x ̅=1.47mg kg-1) > As (x ̅=0.167 mg kg-1) > Hg (x ̅=0.021 mg kg-1), and they did too in the soils, with variation coefficient of Hg, Pb, Cr, Cd and As (%) being 99.99, 305.9, 118.7, 266.8 and 51.74 in the soils, and 58.27, 87.75, 121.2, 87.75 and 71.87 in the plants, respectively, which suggests that absorption of heavy metals by E. adenophorum plants is subject to soil environment. Contents of heavy metals in E. adenophorum plants are positively related to total As, DTPA/HCl extractable Pb, DTPA/HCl extractable Cd, and NaHCO3 extractable As in the soils, with correlation coefficient being 0.528, 0.337 6, 0.761 2 and 0.313 7 (n=38~42), respectively. Among the organs of the plant, stem is the lowest in heavy metal content, root the highest in Cr and As content and leaf the highest in Pb, Cd and Hg content. In the plant Cr and As is not so movable as Pb, Cd and Hg, which move easily from roots to leaves. Compared to most of the 12 plants growing near the E. adenophorum colonies, E. adenophorum plants were lower or similar in heavy metal content, accumulation coefficient and mean and maximum content, which indicates that in the nature E. adenophorum behaves similarly like common plants and does not have any special preference in nutrient or heavy metal absorption and doesn’t support the conclusion drawn by scientists in the past that E. adenophorum is a heavy metal accumulator. Furthermore, heavy metals in the composted E. adenophorum, stems and leaves, were obviously lower than the criteria set in the National Standard for Organic Manure (NY525-2012). 【Conclusion】 E. adenophorum is not a heavy metal accumulator. In E. adenophorum infested areas, the utilization of in-situ composted E. adenophorum plants as organic manure does not pose any heavy metal toxication risk and the risk of translocation of heavy metals between regions and generation of siol pollution is very limited. So this technique is worth extrapolating.